1. Field of the Invention
The present invention relates to a charging member, a process cartridge and an image forming apparatus.
2. Related Art
In an image forming apparatus using an electrophotographic process, first, a surface of an image holding member including a photoconductive photoreceptor made of an inorganic or organic material is charged using a charging apparatus. Laser beam modulated with an image signal is irradiated thereon to form an electrostatic latent image. Thereafter, charged toner is used to develop the electrostatic latent image to form a visualized toner image. Then, the toner image is electrostatically transferred via an intermediate transfer body or directly onto a transfer material such as recording paper, followed by fixing on a recording material to obtain a required reproduction image.
A charging apparatus is an apparatus that plays the role of charging a body to be charged such as an image holding member. The charging apparatus is categorized largely into two types, one of which is a contact charging apparatus that comes into contact directly with an image holding member to charge the image holding member, and the other of which is a non-contact charging apparatus that, without coming into contact with the image holding member, charges the image holding member by applying corona discharge in the proximity of the image holding member. In recent years, charging apparatus that adopt a contact charging process that is free from a byproduct such as ozone or nitrogen oxide generated by discharging are increasing.
A contact charging apparatus includes a charging member that comes into contact directly with a surface of an image holding member and rotates following movement of the surface of the image holding member to charge the image holding member.
When the charging member is used to charge the image holding member, a toner or an external additive of the toner on the image holding member frequently attaches to the charging member. In some cases, such an attachment causes a fluctuation in a surface resistance of the charging member to render charging property unstable.
In this connection, for the purpose of inhibiting the toner or the external additive of the toner from attaching, a technique in which a specific material is used in the outermost layer of the charging member has been proposed
As an characteristic of the contact charging apparatus, improvement in endurance for continuously charging a body to be charged with less fluctuation is demanded. In the contact charging process, when an AC current applied to the charging apparatus is reduced to minimize damage caused by discharge to a photoreceptor, there is a concern that fluctuation in charging becomes larger. Accordingly, in order to inhibit a white spot or a black spot caused by fluctuation in the charging from occurring while reducing damage to an image holding member, a technique in which resin particles are contained in the outermost layer to make a surface irregular to improve uniformity of charging has been proposed.